U.S. patent number 4,611,197 [Application Number 06/703,092] was granted by the patent office on 1986-09-09 for malfunction-detecting status monitoring system.
Invention is credited to Michael J. Sansky.
United States Patent |
4,611,197 |
Sansky |
September 9, 1986 |
Malfunction-detecting status monitoring system
Abstract
A multiple-sensor status monitoring system for monitoring the
status of an area while avoiding false alarms and detecting and
identifying faulty sensors. The system uses a timer and logic to
avoid false alarms by generating an alarm signal only if two
sensors give a response within a preselected interval of time. The
system employs latching storage elements to keep a record of which
of the sensors have made spurious responses, and a visual display
to give a trouble warning respecting those sensors.
Inventors: |
Sansky; Michael J. (San
Clemente, CA) |
Family
ID: |
24823980 |
Appl.
No.: |
06/703,092 |
Filed: |
February 19, 1985 |
Current U.S.
Class: |
340/522;
340/309.16; 340/309.7; 340/506; 340/508; 340/521; 340/523; 340/525;
340/526; 340/527 |
Current CPC
Class: |
G08B
19/005 (20130101); G08B 29/183 (20130101); G08B
29/16 (20130101) |
Current International
Class: |
G08B
19/00 (20060101); G08B 29/00 (20060101); G08B
29/16 (20060101); G08B 29/18 (20060101); G08B
019/00 () |
Field of
Search: |
;340/522,521,506,508,507,523,524,525,527,528,526,309.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Crosland; Donnie L.
Attorney, Agent or Firm: Fulwider, Patton, Rieber, Lee &
Utecht
Claims
I claim:
1. A status monitoring system comprising:
a plurality of status sensors, each operative to provide a primary
signal in response to a stimulus;
storage means associated with each of said sensors, each of said
storage means being responsive to a primary signal from the
associated one of said sensors to store a record of the occurrence
of a primary signal from said associated sensor;
indicator means connected to said storage means, operative to
provide an indication of the storage of a record of the occurrence
of a primary signal;
a plurality of timers, each of said timers being connected to at
least one of said sensors, each of said timers being responsive to
a primary signal from any one of the sensors connected thereto to
provide a timing output signal having a predetermined duration;
and
logic means responsive to said timers to generate a status change
signal when a plurality of said timing output signals are being
provided simultaneously.
2. A status monitoring system according to claim 1, wherein each of
said sensors is connected to one and only one of said timers.
3. A status monitoring system according to claim 1, further
comprising means to render said storage means and said timers
unresponsive to primary signals from their respective associated
sensors.
4. A status monitoring system according to claim 3, further
comprising a delay timing means operative to render said storage
means and timers responsive to primary signals from their
respective associated sensors after a predetermined interval of
time has elapsed.
5. A status monitoring system according to claim 3, further
comprising means to render said storage means responsive to primary
signals from their respective associated sensors.
6. A status monitoring system comprising:
a plurality of status sensors, each operative to provide a primary
signal in response to a stimulus;
storage means associated with each of said sensors, each of said
storage means being responsive to a primary signal from the
associated one of said sensors to store a record of the occurrence
of a primary signal from said associated sensor;
indicator means connected to said storage means, operative to
provide an indication of the storage of a record of the occurrence
of a primary signal;
a plurality of first timing means, one of said timing means being
connected to each of said sensors, each of said first timing means
being operative to generate a secondary signal of predetermined
duration in response to the occurrence of a primary signal from the
associated one of said sensors, the duration of each said secondary
signal being independent of the duration of the associated primary
signal;
a plurality of second timing means, each of said second timing
means being connected to at least one of said first timing means,
each of said second timing means being responsive to a secondary
signal from any one of the first timing means connected thereto to
provide a timing output signal having a predetermined duration;
and
logic means responsive to said second timing means to generate a
status change signal when a plurality of said timing output signals
are being provided simultaneously.
7. A status monitoring system according to claim 6, further
comprising means to render said storage means unresponsive to
primary signals from their respective associated sensors and means
to render said second timing means unresponsive to secondary
signals from their respective associated first timing means.
8. A status monitoring system according to claim 7, further
comprising a delay timing means operative to render said storage
means responsive to primary signals from their respective
assosiated sensors, and to render said second timing means
responsive to secondary signals from their respective associated
first timing means, after a predetermined interval of time has
elapsed.
9. A status monitoring system according to claim 7, further
comprising means to render said storage means responsive to primary
signals from their respective associated sensors.
10. A malfunction-detecting system for reducing false alarms from a
status monitoring system having a plurality of status sensors, each
of said sensors being operative to generate a primary signal in
response to a change in the status being monitored, comprising:
a plurality of storage means, each of said sensors having one of
said storage means connected thereto, each of said storage means
being responsive to a primary signal from the associated one of
said sensors to store a record of the occurrence of a primary
signal from said associated sensor;
indicator means, connected to said storage means, operative to
provide an indication of the storage of a record of the occurrence
of a primary signal by said storage means;
a plurality of timers, each of said timers being connected to at
least one of said sensors, each of said timers being responsive to
a primary signal from any one of the sensors connected thereto to
provide a timing output signal having a predetermined duration;
and
logic means responsive to said timers to generate a status change
signal when a plurality of said timing output signals are being
provided simultaneously.
11. A status monitoring system according to claim 10, further
comprising means to render said storage means and said timers
unresponsive to primary signals from their respective associated
sensors.
12. A status monitoring system according to claim 11, further
comprising a delay timing means operative to render said storage
means and timers responsive to primary signals from their
respective associated sensors after a predetermined interval of
time has elapsed.
13. A status monitoring system according to claim 11, further
comprising means to render said storage means responsive to primary
signals from their respective associated sensors.
14. A status monitoring system according to claim 10, wherein said
storage means comprises a silicon-controlled rectifier wired in a
latch circuit, and said indicator means comprises a visual
indicator.
15. A status monitoring system according to claim 10, wherein said
second timing means each comprises a monostable multivibrator.
16. A malfunction-detecting system for reducing false alarms from a
status monitoring system having a plurality of status sensors, each
of said sensors being operative to generate a primary signal in
response to a change in the status being monitored, comprising:
a plurality of storage means, each of said sensors having one of
said storage means connected thereto, each of said storage means
being responsive to a primary signal from the associated one of
said sensors to store a record of the occurrence of a primary
signal from said associated sensor;
indicator means connected to said storage means, operative to
provide an indication of the storage of a record of the occurrence
of a primary signal;
a plurality of first timing means, one of said timing means being
connected to each of said sensors, each of said first timing means
being operative to generate a secondary signal of predetermined
duration in response to the occurrence of a primary signal from the
associated one of said sensors, the duration of each said secondary
signal being independent of the duration of the associated primary
signal;
a plurality of second timing means, each of said second timing
means being connected to at least one of said first timing means,
each of said second timing means being responsive to a secondary
signal from any one of the first timing means connected thereto to
provide a timing output signal having a predetermined duration;
and
logic means responsive to said second timing means to generate a
status change signal when a plurality of said timing output signals
are being provided simultaneously.
17. A status monitoring system according to claim 16, further
comprising means to render said storage means unresponsive to
primary signals from their respective associated sensors and means
to render said second timing means unresponsive to secondary
signals from their respective associated first timing means.
18. A status monitoring system according to claim 17, further
comprising a delay timing means operative to render said storage
means responsive to primary signals from their respective
associated sensors, and to render said second timing means
responsive to secondary signals from their respective associated
first timing means, after a predetermined interval of time has
elapsed.
19. A status monitoring system according to claim 17, further
comprising means to render said storage means responsive to primary
signals from their respective associated sensors.
20. A status monitoring system according to claim 16, wherein said
storage means comprises a silicon-controlled rectifier wired in a
latch circuit, and said indicator means comprises a visual
indicator.
21. A status monitoring system according to claim 16, wherein said
second timing means each comprises a monostable multivibrator.
22. An improvement to a multiple-sensor alarm system having a
plurality of sensors, each of said sensors being operative to
generate a primary signal in response to a stimulus, said alarm
system being operative to generate a first alarm signal immediately
upon the activation of a predetermined one of said sensors and a
second alarm signal a predetermined time after the activation of
said predetermined sensor, said alarm system also being operative
to generate said second alarm signal in response to the activation
of any of the others of said sensors, said alarm system also being
operative to generate an armed signal when said system has been
activated, said improvement comprising:
delay timing means, responsive to said armed signal, operative to
generate an active signal after said armed signal has been present
a predetermined interval of time;
a plurality of storage means, one of said storage means being
connected to each of said sensors except said predetermined one,
each of said storage means responsive to a primary signal from the
associated one of said sensors to store a record of the occurrence
of a primary signal from said associated sensor;
indicator means connected to said storage means, operative to
provide an indication of the storage of a record of the occurrence
of a primary signal;
a plurality of first timing means, one of said first timing means
being connected to each of said sensors except said predetermined
one, each of said timing means being operative to generate a
secondary signal of predetermined duration in response to the
occurrence of a primary signal from the associated one of said
sensors, the duration of each said secondary signal being
independent of the duration of the associated primary signal;
a plurality of second timing means, each of said second timing
means being connected to at least one of said first timing means,
each of said second timing means being responsive to a secondary
signal from any one of the first timing means connected thereto to
provide a timing output signal having a predetermined duration;
logic means responsive to said second timing means to generate a
status change signal having characteristics similar to the
characteristics of a primary signal as generated by said sensors
when a plurality of said timing output signals are being provided
simultaneously;
means to prevent the generation of said status change signal unless
said active signal is present and said first alarm signal is not
present; and
means to render said storage means unresponsive to primary signals
from their respective associated sensors unless said active signal
is present and said first alarm signal is not present.
23. The improvement according to claim 22, further comprising means
to render said storage means responsive to primary signals from
their respective associated sensors in the absence of said active
signal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to status monitoring systems such as
burglar or fire alarm systems, and more particularly to status
monitoring systems employing multiple sensors and special logic to
reduce the probability of false alarms.
2. The Prior Art
Status monitoring systems using multiple sensors and logic
circuitry to discriminate against false alarms are known to the
art. Such logic circuitry generally accomplishes its function of
avoiding false alarms by generating an alarm signal only if two or
more of the sensors generate response signals within a
predetermined interval of time. An example of such a system is
found in U.S. Pat. No. 4,195,296, dated Mar. 25, 1980, issued to
Galvin.
A problem with existing multiple-sensor status monitoring systems
is the failure of such systems to give a trouble signal if a sensor
malfunctions. A sensor malfunction may take the form either of a
failure to respond to a stimulus or of a spurious response in the
absence of a stimulus. The first kind of malfunction--failure to
respond at all--can result in a failure to sound the alarm when the
status being monitored changes. The second kind of malfunction--a
spurious response--can result in a false alarm. Neither kind of
sensor malfunction produces a trouble warning in existing
multiple-sensor status monitoring systems, and hence there is no
way to know that one or more sensors have malfunctioned until one
or the other kind of system failure occurs.
Moreover, even if there is a system failure, if a sensor is
malfunctioning intermittently there is no way to determine which of
the various sensors is the cause of the trouble, and hence
troubleshooting such a system failure is virtually impossible.
A partial solution to the problem of generating a trouble warning
in the event of the first kind of sensor malfunction--failure to
respond at all--is disclosed in U.S. Pat. No. 3,801,978, issued
Apr. 2, 1974 to Gershberg. The Gershberg patent discloses an
intrusion alarm system comprising the combination of a microwave
motion sensor and an ultrasonic motion sensor. False alarms are
avoided by activating an alarm only if both sensors simultaneously
signal the presence of an intruder. The alarm is also activated if
either sensor fails to function, but only a complete failure of
either the microwave or the ultrasonic sensing signal causes alarm
activation. So long as both sensors are radiating sensing signals,
the failure of either sensor to respond to a proper stimulus will
not be detected. A further limitation of the Gershberg system is
that even in the event of a complete failure of one of the sensing
signals, the Gershberg system does not identify the sensor that has
failed.
Even the limited failure-detecting ability of the apparatus
disclosed by Gershberg only works with an energy radiating sensor
such as a microwave or ultrasonic motion detector. A passive sensor
is not adaptable to being monitored by the Gershberg apparatus, and
hence a failure of a passive sensor will not be detected by such
apparatus.
A spurious response in the absence of a proper stimulus is easy to
detect in a single-sensor status monitoring system because such a
response activates the system's alarm. Since there is only one
sensor, locating the fault is relatively simple once it has been
determined that the alarm was a false alarm. However, a
multiple-sensor system--even the Gershberg system--does not
activate its alarm if it detects a response signal from only one
sensor. A spurious response signal from any one sensor, regardless
of whether the signal is continuous or intermittent, is simply
ignored. Hence, since there is neither an alarm nor a trouble
warning, the defective sensor will continue to malfunction and
system performance will be degraded.
A partial solution to the problem of detecting a spurious response
from one sensor is proposed in the multiple-sensor system disclosed
in the Galvin patent. The Galvin system has logic circuitry to
generate a first alarm signal if any one sensor is activated and to
generate a second alarm signal only if at least two sensors are
activated within a predetermined interval of time. Thus, if the
first alarm, but not the second alarm, sounds, once it has been
determined that the alarm was false, it will be apparent that one
of the sensors has given a spurious response. However, in Galvin's
apparatus there is no way to determine which sensor has caused the
trouble.
It will be apparent from the foregoing that there is a need for a
multiple-sensor status monitoring system having the ability to warn
of a sensor malfunction either of the first kind or of the second
kind and to identify the malfunctioning sensor. The present
invention satisfies this need.
SUMMARY OF THE INVENTION
The present invention resides in a multiple-sensor status
monitoring system. The system has a plurality of sensors that each
provide a primary signal in response to a stimulus. A storage means
coupled to each sensor keeps an electronic record of the occurrence
of a primary signal from that sensor. In addition, each sensor is
connected to one of a plurality of timers, and each timer provides
a timing output signal of fixed duration in response to a primary
signal from any of the sensors connected to that timer. A logic
means connected to the timers generates a status change signal if a
timing output signal from one timer overlaps such a signal from any
other timer. Thus, an alarm is sounded only if at least two sensors
provide primary signals within a predetermined time of each
other.
A sensor malfunction manifested by the generation of spurious
responses from a sensor can be detected by examining the record
kept by the storage means of primary signals provided by each
sensor. A sensor malfunction manifested by a failure to respond to
a valid stimulus can be detected by deliberately introducing a
stimulus throughout the area being monitored and then determining
from the record which sensors failed to provide primary signals in
response to the stimulus.
In one embodiment, the storage means takes the form of a plurality
of silicon-controlled rectifiers ("SCRs"), one for each sensor,
wired into simple latch circuits. A primary signal from a given
sensor latches the SCR associated with that sensor; once latched,
the SCR stays latched until it is manually reset. Indicator means
associated with each latch may take the form of a light-emitting
diode ("LED") to indicate latching.
The timers and logic circuit prevent a status change alarm signal
from being generated unless at least two different sensors provide
primary signals within a predetermined period of time. Some of the
sensors are connected to one timer and some to each of the other
timers. If a sensor provides a primary signal, then the timer to
which that sensor is connected generates a timer output signal
having a duration of about three minutes. If a sensor connected to
another timer also provides a primary signal, then that other timer
also generates a timer output signal. The logic circuit generates a
status change alarm signal only if output signals from both timers
overlap in time. During initial system design, the sensors are laid
out such that a bona fide change in status will of necessity cause
primary signals to be provided by at least two different sensors,
not all of which are connected to the same timer. In this way, the
probability of false alarms is greatly reduced because a spurious
signal from any one sensor will not sound the alarm, but signals
from two sensors within three minutes of each other will sound the
alarm.
In another embodiment, a circuit is provided that can "freeze" all
the latches and timers, rendering them insensitive to primary
sensor signals. This feature is desirable if the invention is
embodied in a burglar alarm having a control panel located within
the protected area. Typically, a burglar alarm is only activated
during hours when the premises being guarded are deserted. When the
premises are opened, it is necessary for a person to enter the
protected area and proceed to the control panel to shut off the
alarm. By making such an entry and walking through the protected
area to the control panel, the person will of necessity activate
one or more of the sensors, but it is not desirable for a record of
such activations to be stored by the latches. Accordingly, the
freeze circuit can be activated so that the person can enter the
premises and shut off the alarm without either sounding the alarm
or causing a record of sensor activations to be stored in the latch
circuits.
In still another embodiment, an exit delay circuit is provided.
This circuit "freezes" the timers and latches for a predetermined
interval of time after the alarm system has been turned on, so that
the person who turns the system on has time to leave the protected
area without setting off the alarm.
It will be appreciated from the foregoing that the present
invention represents a significant advance in the field of
multiple-sensor status monitoring systems. In particular, a status
monitoring system incorporating this invention gives a trouble
warning in the event any of its sensors gives a spurious response
and identifies which sensor or sensors have given such responses.
The system is also capable of detecting and identifying non
responsive sensors during system testing.
Other aspects and advantages of the present invention will become
apparent from the following more detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a multiple-sensor status monitoring
system according to the invention;
FIG. 2 is a schematic diagram of the circuitry contained within box
2 of FIG. 1;
FIG. 3 is a block diagram of a multiple-sensor status monitoring
system that is similar to the system shown in FIG. 1 except for the
addition of an exit delay circuit and a circuit to prevent sensor
activations if a first alarm signal has been generated;
FIG. 4 is a schematic diagram of the circuitry contained within box
2A of FIG. 3;
FIG. 5 is a block diagram of a multiple-sensor status monitoring
system according to the prior art; and
FIG. 6 is a block diagram of the multiple-sensor status monitoring
system of FIG. 5, with circuitry embodying the present invention
added thereto as an improvement.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Multiple-sensor status monitoring systems with logic for avoiding
false alarms give no warning of the failure of any one sensor. The
present invention provides a multiple-sensor status monitoring
system that stores and displays a record of the primary signals
provided by each sensor but sounds no alarm unless two or more
different sensors generate primary signals within a predetermined
interval of time.
A multiple-sensor status monitoring system 100 embodying the
present invention has sensor inputs 101, 103, 105 and 107, as shown
in FIG. 1. Each input is configured for connection to a sensor,
such as a normally-closed switch, that presents a closed circuit to
ground when said sensor is not activated and an open circuit when
said sensor is activated, the primary signal provided by such a
sensor being the interruption of the connection between ground and
the input to which said sensor is connected. It will be apparent to
those skilled in the art, however, that said inputs could be
configured to accept other kinds of primary signals if desired.
Sensor input 101 is connected to a latch circuit 109 through a
conductor 111. In similar fashion, sensor inputs 103, 105 and 107
are connected to identical latch circuits 113, 115 and 117 through
conductors 119, 121 and 123, respectively.
Typical latch circuit 109, shown schematically in FIG. 2, has a
silicon-controlled rectifier ("SCR") 125 that is held quiescent by
bias resistors 127, 129 and 131 until a sensor connected to input
101 provides a primary signal to the gate of SCR 125, and then SCR
125 begins to conduct, causing a voltage to develop across resistor
133 in the cathode circuit of SCR 125. Said voltage is applied to
the base of transistor 135, and emitter current begins to flow.
Said emitter current flows through current limiting resistor 139
and light-emitting diode ("LED") 137, and LED 137 begins to emit
light. Once SCR 125 begins to conduct, it continues to conduct
regardless of the status of the sensor connected to input 101, and
hence LED 137 remains lit, thereby giving a continuous indication
that a primary signal was received from said sensor.
In like manner, latch circuits 113, 115 and 117 are triggered by
primary sensor signals occurring at inputs 103, 105 and 107,
respectively, and LEDs associated with said latch circuits are
illuminated in similar fashion.
Input 101 is connected to timer 145 through conductor 147, and
input 103 is connected to timer 145 through conductor 149. A
primary signal at input 101 is applied to a one-shot multivibrator
comprising transistor 151, resistor 153, and capacitor 155, causing
the multivibrator to produce a short output pulse that is applied
to pin 2 of a pulse generator comprising a type 555 integrated
circuit 157, resistor 159, capacitor 161, and time constant
determinants resistor 163 and capacitor 165. In like manner, a
primary signal at input 103 is applied to an identical one-shot
multivibrator comprising transistor 167, resistor 169 and capacitor
171, causing a short output pulse to be applied to pin 2 of
integrated circuit 157.
Upon receiving a short input pulse from either of said
multivibrators, integrated circuit 157 provides at conductor 173 a
timer output signal having a duration governed by resistor 163 and
capacitor 165. In similar fashion, inputs 105 and 107 are connected
through conductors 175 and 177, respectively, to identical timer
179, and a primary signal from either input 105 or 107 results in a
timer output signal at conductor 181.
Although the duration of the timer output signals is not critical,
for a typical burglar alarm installation a duration of about three
minutes gives good results.
Timer output signals from timers 145 and 179 are applied to logic
block 183. Logic block 183 includes NAND gate 185, resistors 187
and 189, and output transistor 191. When the circuit is at rest,
the output of gate 185 is high, causing transistor 191 to appear as
a closed circuit to ground at output 193. A timer output signal
from only one of timers 145 and 179 will not change this status,
but if at any moment timer output signals from both said timers are
simultaneously present at the inputs to gate 185, then transistor
191 will appear as an open circuit at output 193, and this
appearance as an open circuit constitutes a status change output
signal.
The probability of a false alarm is reduced by causing transistor
191 to switch to an open circuit from a closed circuit to ground
only if two different sensors provide primary signals within a
predetermined time set by time constant components 163 and 165 and
by the comparable components in timer 179. If a sensor malfunctions
so as to provide a continuous primary signal, the multivibrator
that couples that sensor to its associated timer blocks such a
continuous signal from interfering with normal operation of the
timer and the other sensors connected thereto.
An embodiment of the invention having certain additional features
that are especially desirable in burglar alarm systems is shown in
block form in FIG. 3. This embodiment is similar to that shown in
FIG. 1 and for convenience components in FIG. 3 that are similar to
components in FIG. 1 are assigned the same reference numerals,
analogous but changed components are assigned the same reference
numerals accompanied by the letter "A", and different components
are assigned different numerals.
A multiple-sensor status monitoring system 100A has sensor inputs
101, 103, 105 and 107 connected to identical latch circuits 109A,
113A, 115A and 117A through conductors 111, 119, 121 and 123,
respectively.
Latch circuit 109A, shown schematically in FIG. 4, is similar to
latch circuit 109 as shown in FIG. 2 except that cathode resistor
133 of SCR 125, instead of connecting directly to ground, connects
through diode 195 to exit delay circuit 197 through conductor 199.
Identical latch circuits 113A, 115A and 117A are also connected to
exit delay circuit 197 in a like manner.
Exit delay circuit 197 has input 201, type 555 IC 203, time
determinants 205 and 207, transistor 209, and resistor 211.
Initially, input 201 is kept at ground level, causing output pin 3
of IC 203 to be at ground level. Transistor 209 is cut off, no
current can flow through conductor 199, and latches 109A, 113A,
115A and 117A are prevented from latching whether or not primary
sensor signals are presented to their inputs. If a positive voltage
is applied to input 201, output pin 3 of IC 203 goes to a positive
level after a period of time determined by components 205 and 207.
Once output pin 3 goes to a positive level, transistor 209 switches
on, providing a path from conductor 199 to ground and enabling
latches 109A, 113A, 115A and 117A to latch in response to primary
sensor signals.
Timer circuit 145A, shown schematically in FIG. 4, and identical
timer circuit 179A are similar to timers 145 and 179 as shown in
FIGS. 1 and 2, except that reset pin 4 of IC 157 is used to control
operation of timer 145A and reset pin 4 of the corresponding IC in
timer 179A is used to control operation of timer 179A. Reset pins 4
of both ICs are connected to output pin 3 of IC 203 in exit delay
circuit 197, and, as long as said pin 3 remains at ground level,
timers 145A and 179A cannot function. Only after said pin 3 goes to
a high level can either timer generate a timer output signal in
response to primary signals from the associated sensors.
Exit delay circuit 197, then, activates the system a predetermined
time after a positive voltage is applied to input 201. This makes
it possible for a person to turn the system on at a control panel
located within the protected premises, and then to leave the
building without setting off the alarm.
Sensor inputs 101, 103, 105 and 107 are also connected to freeze
circuit 213 through diodes 215, 217, 219 and 221, respectively. So
long as input 223 to freeze circuit 213 is kept at ground level,
transistor 225 remains cut off and has no effect on the performance
of the system. If a positive voltage is applied to input 223 and
from there to the base of transistor 225 through resistor 227,
transistor 225 turns on, effectively grounding the cathodes of
diodes 215, 217, 219 and 221. Grounding said cathodes has the
effect of shorting inputs 101, 103, 105 and 107 to ground and
thereby rendering the system insensitive to primary sensor signals
applied to any of said inputs. This circuit is useful to prevent
activation of the alarm system when a person desires to walk
through the protected area to turn off the system. By applying a
positive voltage to input 223, the system is rendered insensitive
to primary sensor signals; however, any latches that have
previously been latched remain latched even though freeze circuit
213 has been activated, so that the operator can tell by observing
the LEDs which of the sensors provided primary signals during the
hours the system was in operation. This information tells which
sensors have given spurious responses and makes quick, efficient
repair possible.
After the operator has observed which LEDs are illuminated, the
system is turned off by removing the positive enabling voltage from
input 201. If it is desired to test the sensors for proper
operation, switch 229 is closed by the operator, enabling the latch
circuits, but not the timers, to function. Then a stimulus is
deliberately introduced throughout the protected area, and the
operator observes the LEDs to see which ones are lit. If a LED
remains unlit, the operator knows that the associated sensor failed
to respond to the stimulus, and repairs can be effected.
A particularly useful embodiment of the present invention comprises
a unit that can be retrofitted to an existing status monitoring
system, such as a burglar alarm. Such an existing, prior art status
monitoring system 500, illustrated in block form in FIG. 5, has
sensors 501, 503, 505 and 507 connected to sensor input 509 of
alarm panel 511 and sensor 513 connected to special sensor input
515. When an operator desires to activate the system, switch 517 is
turned to position #3 and an active signal is thereby applied to
LED 519 through connection 521 to indicate that the system is
active. An internal timing element (not shown) delays actual system
activation for a short period of time to permit the operator to
leave the premises without setting off the alarm, and thereafter,
if any of sensors 501, 503, 505 or 507 provides a primary signal by
momentarily becoming an open circuit, an alarm output signal is
provided at terminal 522 to activate a suitable alarm such as alarm
bell 523.
A primary signal from sensor 513 has a different effect. If sensor
513 provides a primary signal by becoming an open circuit, an alert
signal device 525, such as a buzzer or warning light, is activated
by an alert signal at output 527, and unless the alarm system is
turned off within a predetermined time thereafter, alarm 523 is
sounded. However, once sensor 513 has provided a primary signal,
the system is rendered unresponsive to primary signals from any of
the other sensors. Sensor 513 is so located that the operator
activates it upon entering the building, and so long as the
operator proceeds directly to panel 511 and shuts off the system
within said predetermined time, alarm 523 will not be sounded. The
system is turned off by turning switch 517 to position #2 (standby)
or #1 (power off).
Multiple-sensor status monitoring system 100A can be connected to
existing burglar alarm system 500 to form a complete
multiple-sensor burglar alarm system having all the advantages of
the present invention, as shown in FIG. 6. Sensors 501, 503, 505
and 507 are disconnected from terminal 509 of burglar alarm 500 and
are instead connected to inputs 101, 103, 105 and 107 of monitoring
system 100A. Terminal 521 of burglar alarm 500 is connected to
input 201 of monitoring system 100A, so that an active signal at
terminal 521 starts the exit delay timer of monitoring system 100A.
Terminal 527 of burglar alarm 500 is connected to input 223 of
monitoring system 300, so that an alert signal from burglar alarm
500 activates the freeze circuit of monitoring system 100A. Output
193 of monitoring system 100A is connected to sensor input 509 of
burglar alarm 500. Finally, operating power for monitoring system
100A can be drawn from power terminals 529 and 531 of burglar alarm
500.
When the complete multiple-sensor burglar alarm system is in
operation, an operator can activate the system, as before, by
setting switch 517 to position #3. The operator then has a short
interval of time within which to leave the protected area without
setting off the alarm. Thereafter, if both timer 145A and timer
179A of monitoring system 100A produce overlapping timer output
signals, a status change signal is applied to input 509 and the
alarm sounds. The latches and LEDs of monitoring system 100A tell
which sensors have provided primary response signals. When the
operator returns and wishes to shut off the complete system, sensor
513 is activated, causing an alert signal to be applied to input
223 and thereby rendering system 100A insensitive to any further
sensor activations.
It will be apparent from the preceding description that this
invention provides a multiple-sensor alarm system having not only
the ability to avoid false alarms but also the ability to warn of
sensor failures and to identify the failed sensor or sensors for
repair or replacement. Such a multiple-sensor system is provided
either as a stand-alone system or as a retrofit to be added to an
existing alarm system not having these desirable features.
Although one specific embodiment of this invention has been
described and illustrated, it is to be understood that the
invention is not to be limited to the specific forms or
arrangements of parts so described and illustrated, and that
various changes can be made within the scope of the invention. It
is therefore to be understood that, within the scope of the
appended claims, the invention may be practiced otherwise than as
specifically described.
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